Okay, thanks. Looks like this is an incompatibility between the SugarCube update we applied and the itch app, which is using a 2018 Javascript standard. We can address it on our end, I'll just have to consult with majou who maintains our SugarCube mod, so it'll probably be later today or tomorrow.
You could also try the beta/dev version of the itch app which is on a newer Javascript standard: